Hello, look the truth I do not know what the error codes that you say mean, it would be convenient that you take into consideration what type of failure is ..... and taking into account how you say that the spark plug 4 fails, notice there the problem, being able to be due to excess fuel (bad combustion and black spark plug), by non -injection (problem in the injection perhaps), motor compression problem Dry), I need you to tell me that the error codes and the state that is the spark plug 4.
Also as a reference point, I do not know if it will be the case, the Chevrolet vehicle OPTRA Motor 1.6, presents failures in its engine, some not all of themselves, that in this case if it presents problems such as something like like this P0300 codes and the like, it is said that there are problems in the engine. I hope to help you in something.